JACKSONVILLE, Fla. — CSX Transportation’s operations may be stabilizing, but the railroad’s detailed presentation to federal regulators this week revealed just how far service had fallen in the past month as congestion built in key terminals on its western corridor.

On-time train arrivals – which reached an all-time high of 88 percent in May, up from 66 percent last year – tumbled to around 55 percent over the past four weeks. And over that period more than a quarter of all carloads failed to make the right train as scheduled, compounding the delays for shippers.

The railroad began struggling in mid July amid the broad operational changes CEO E. Hunter Harrison has made while implementing precision scheduled railroading. Two ill-timed major derailments in recent weeks only hurt the railroad’s operational performance.

Shippers have been complaining to Congress and federal regulators regarding widespread service disruptions. The erratic service has caused plant shutdowns and production slowdowns while forcing some CSX customers to resort to diverting shipments to trucks.

The Surface Transportation Board has responded by requiring CSX to report much more detailed performance metrics, beginning this week. And by Thursday CSX will have to submit a schedule of changes it will make to its operating plan during the remainder of this year.

CSX on Monday told the STB its network metrics have improved somewhat since the height of its operational challenges over the past couple of weeks. Average train speed is up slightly and overall terminal dwell is down a bit.

CSX reopened the hump at Avon Yard in Indianapolis last week to improve service and prevent congestion at secondary yards. “We might have made a mistake there,” by shutting down the hump, Harrison told The Wall Street Journal.

Reactivating Avon, along with other tweaks to the operating plan, pushed down terminal dwell considerably at five western terminals. Cars spent 33 hours in those terminals last week on average, down from a peak of nearly 53 hours two weeks ago.

The railroad’s presentation to the STB hinted it is still trying to find the right balance between hump yards and flat-switching terminals. The “absolute number of humps [is] not ‘good’ or ‘bad’; rather, a different configuration of handling traffic,” the presentation says. But the productivity of remaining hump yards has improved since June 30.

CSX has not yet converted Selkirk Yard, near Albany, N.Y., to a flat-switching facility. In May CSX said it was transitioning Selkirk to a flat-switching yard, as it has done at seven of its dozen hump yards. A spokesman says the railroad continues to evaluate Selkirk operations.

The railroad says network fluidity has improved “meaningfully” over the past two weeks and that it should continue to improve. Harrison has told the STB that he expects more noticeable service improvements after Labor Day.

CSX continues to whittle away at a backlog of customer inquiries. Most of those inquiries, CSX says, deal with delayed cars. CSX has dispatched customer service personnel to locations with significant service problems, including Columbus, Ohio; Russell, Ky.; Indianapolis; and Memphis, Tenn.

CSX also said many of the STB’s requests – including local service metrics and figures for train origination and arrival – do not necessarily mesh with what’s important in precision scheduled railroading.

The railroad said, for example, that, “holding a train’s origination to allow additional cars to reach a customer on time...would hinder train origination and arrival metrics, but provide better service to the customer.”

CSX also assured federal regulators that it had enough locomotives and crews available to handle its current traffic levels. The railroad had 3,275 active locomotives last week, down 488 units from the first-quarter average. It has pulled some units out of storage to help power an uptick in coal traffic.

The railroad’s car order fulfillment statistics are a case study in what happens when service slides. Customers order more cars than they need, hoping that what is delivered is close to the actual number needed.

CSX says car orders spiked 40 percent in the third quarter when compared to the first quarter.

“Order levels have disconnected from demand,” CSX says.

When the numbers were normalized, CSX provided cars as scheduled between 70 and 85 percent of the time.